ROOST (3)

Roost, n. [[AS. hrōst; akin to OD. roest roost, roesten to roost, and probably to E. roof. Cf. Roof.]] 1. 1. The pole or other support on which fowls rest at night; a perch.
He clapped his wings upon his roost. Dryden. 2. 2. A collection of fowls roosting together.
At roost, on a perch or roost; hence, retired to rest.